Abnormal Epithelium and Histology

  • Understanding epithelial tissues is essential for recognizing various abnormalities.

Cell Characteristics

  • Basic Unit of Life: All organisms are formed from cells.
  • Tissue Formation: Cells create tissues and organs through division.

Cell Functions

  • Layer Formation: Forms protective layers covering surfaces.
  • Nutrient Storage: Stores nutrients and energy.
  • Movement Production: Facilitates movement in various contexts.
  • Connection Creation: Forms connections between different tissues.
  • Protection against Pathogens: Acts as a barrier to pathogens.
  • Information Communication: Involves mechanisms for cell signaling.
  • Reproduction: Supports processes necessary for cell reproduction.

Cell Structure

  • Plasma membrane: Outermost layer, controls entry/exit.
  • Cytoplasm: Contains cytosol and organelles.
  • Nucleus: Contains chromatin and nucleolus, imperative for genetic information.
  • Organelles:
    • Endoplasmic Reticulum (ER): Produces lipids and transports molecules.
    • Ribosomes: Site of protein synthesis.
    • Golgi Apparatus: Modifies, sorts, and packages proteins.
    • Mitochondria: Powerhouse of the cell, produces ATP.
    • Lysosomes and Peroxisomes: Involved in detoxification and breakdown of waste products.
    • Cytoskeleton: Composed of microtubules, intermediate filaments, and microfilaments, providing structural support.

Four Types of Tissue

  1. Epithelial Tissue: Covers surfaces (e.g., skin, lining of organs).
  2. Connective Tissue: Provides support and structure (e.g., bone, fat).
  3. Muscle Tissue: Enables movement (e.g., cardiac, smooth, skeletal).
  4. Nervous Tissue: Lastly, facilitates communication across the body (e.g., brain, nerves).

Characteristics of Epithelial Tissue

  • Cell Density: Highly cellular with minimal extracellular matrix.
  • Polarity: Contains an apical and a basal surface.
  • Basement Membrane Attachment: Connects epithelial tissue to underlying connective tissue.
  • Avascularity: Lacks blood vessels; nutrients diffuse from underlying tissues.
  • Regeneration Capacity: High regenerative capability, replacing damaged cells rapidly.

Functions of Epithelial Tissue

  • Protection: Provides a physical barrier from pathogens and injury.
  • Selective Permeability: Controls what substances can pass through.
  • Secretion: Produces various substances (mucus, hormones, etc.).

Intercellular Junctions

  • Tight Junctions: Prevents passage of molecules between cells, maintains polarity.
  • Gap Junctions: Allows communication between adjacent cells through connexons.
  • Anchoring Junctions (Desmosomes): Provides mechanical strength through cadherins and intermediate filaments (e.g., keratin).

Classification of Epithelia

  • By Cell Shape
    • Squamous (flat)
    • Cuboidal (cube)
    • Columnar (column)
  • By Layering
    • Simple (single layer)
    • Stratified (multiple layers)
    • Pseudostratified (appears layered)

Types of Epithelium and Their Functions

  1. Simple Squamous Epithelium:
    • Functions: Diffusion, filtration.
    • Locations: Lungs, blood vessels, serous membranes.
  2. Simple Cuboidal Epithelium:
    • Functions: Absorption, secretion.
    • Locations: Kidney tubules, glands.
  3. Simple Columnar Epithelium:
    • Functions: Absorption, secretion, movement (ciliated).
    • Locations: Lining of stomach, intestines, uterine tubes.
  4. Pseudostratified Columnar Epithelium:
    • Functions: Protection, movement (ciliated).
    • Locations: Lining of respiratory tract.
  5. Stratified Squamous Epithelium:
    • Functions: Protection.
    • Locations: Skin, oral cavity, esophagus.
  6. Transitional Epithelium:
    • Functions: Distention and relaxation.
    • Locations: Lining of ureters, bladder.

Glandular Epithelium

  • Endocrine Glands: Ductless glands that secrete hormones into the bloodstream.
  • Exocrine Glands: Glands with ducts that secrete substances onto epithelial surfaces.
    • Types of Secretion:
    • Merocrine: Secretions through vesicles (e.g. sweat glands).
    • Apocrine: Secretions involve a portion of the cell (e.g. mammary glands).
    • Holocrine: Whole cell dies and becomes secretion (e.g. sebaceous glands).

Connective Tissue Overview

  • Structure: Sparse cells with an extensive extracellular matrix (protein fibers and ground substance).
  • Functions: Physical protection, support, binding, storage, transportation (e.g. blood), immune protection.

Types of Connective Tissue

  1. Fluid Connective Tissue: Blood and lymph, derived from mesenchyme.
  2. Connective Tissue Proper: Includes dense and loose tissue types (e.g. areolar, adipose, reticular).
  3. Supporting Connective Tissue: Includes cartilage and bone with varying degrees of flexibility and support.

Adipose Tissue**:

  • Structure: Adipocytes in a loose matrix.
  • Functions: Energy storage, protects, insulates.
  • Locations: Surrounds organs, subcutaneous tissue.

Marfan Syndrome**:

  • Genetic condition affecting connective tissue, involves abnormalities in fibrillin.
  • Symptoms include long limbs and structural anomalies, increasing cardiovascular risks.

Scurvy**:

  • Nutritional deficiency caused by lack of Vitamin C, leading to weakened collagen fibers and poor healing.

Gangrene**:

  • Condition often affecting limbs due to insufficient blood flow, potentially from mechanical injury, infection, or diabetes.